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# contrastStretch(destination:)

Stretches the histogram of an 8-bit-per-channel, 4-channel interleaved pixel buffer.

```
func contrastStretch(destination: vImage.PixelBuffer<vImage.Interleaved8x4>)
```

## Parameters

`destination`

The destination pixel buffer.

## Discussion

Use this function to evenly distributes a histogram’s pixel values across the full range of available pixel values.

For example, the following code stretches the contrast of an image:

```swift
let srcImage =  imageLiteral(resourceName: " ... ").cgImage(
    forProposedRect: nil,
    context: nil,
    hints: nil)!

var cgImageFormat = vImage_CGImageFormat(
    bitsPerComponent: 8,
    bitsPerPixel: 8 * 4,
    colorSpace: CGColorSpaceCreateDeviceRGB(),
    bitmapInfo: CGBitmapInfo(rawValue: CGImageAlphaInfo.noneSkipFirst.rawValue))!

let buffer = try vImage.PixelBuffer(
    cgImage: srcImage,
    cgImageFormat: &cgImageFormat,
    pixelFormat: vImage.Interleaved8x4.self)

buffer.contrastStretch(destination: buffer)

let outputImage = buffer.makeCGImage(cgImageFormat: cgImageFormat)
```

## See Also

  <doc://com.apple.accelerate/documentation/Accelerate/enhancing-image-contrast-with-histogram-manipulation>


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